This invention, in one of its aspects, relates to industrial washers. In a more specific aspect the invention pertains to an industrial washer having a longer than normal life. In still another of its embodiments the invention provides a multistage spray washer having a unique housing-supporting framework.
Washers for cleansing metal parts, filters, quartz tubes and the like are described in U.S. Pat. No. 4,299,245, 4,294,271, 3,998,656, 3,741,153, 3,624,750, 3,442,273, 3,174,490, 3,073,325, 2,756,455, and 2,471,506. These washers are either drum washers, or they are spray washers in the form of cabinets equipped with rotating means such as turntables disclosed in U.S. Pat. No. 4,299,245 and 4,294,271. The washers contemplated herein are not cabinets. Rather, they more closely resemble the powder spray booth of 4,928,624, but with liquid collecting means in its base, somewhat along the lines of the paint and varnish stripping system in 4,768,533.
By industrial washers we mean washers adapted for assembly line cleaning of metal parts, usually multistage units using different solutions in each stage for cleaning, chemically treating, and preparing surface of fabricated metal articles. Separate treating zones lead to the highly cleaned metal surfaces required by many coating processes. An an example, one industrial washer with which this invention is concerned is a five stage unit. Unlike prior art cabinets such units include a long room-like housing of steel panels bolted or welded to a framework. A conveying means in its ceiling, and access openings in its ends permit continuous transport of fabricated metal articles therethrough. Tanks are disposed in the base of the washer for washing chemicals. Drainboards separate the chemical tanks, and heat exchangers are provided for the tanks, along with spray manifolds, sprays, exhaust means, pumps, and conveyors for the metal parts being treated. Some stages operate at high temperatures, while others operate under ambient conditions. Processes in which the metal articles thus cleaned will be used include those utilizing powders such as plasma coating techniques, and electrostatic procedures, as well as coating processes utilizing liquids such as organic coating compositions, say, paints, lacquers, resins, varnishes, and the like.
Traditionally each stage of a multistage washer represents a specific process. Some of the stages utilize only ambient rinse water (tap water), whereas others are adapted to handle low concentrations of chemicals. As an example caustics, or alkalies are employed in the first stages. Iron or zinc phosphates are used in third stages, and dilute phosphoric acid in fifth stages, with rinse stages in-between. Variations include additional stages in which dilute muriatic acid, sulfuric acid, and deionized water can be used. Deionized water is especially preferred for use in the last stage.
It is to be emphasized that the chemical cleaning agents utilized in industrial spray washers have a significant corrosive effect on the washer equipment. Since the chemicals employed are either alkaline or acidic in nature, and since they are accompanied by high volumes of moisture there is a generally consistent pattern of washer degradation over the life of the equipment. This has been found to be the case even when the washer is fabricated of stainless steel. Generally multistage spray washers are fabricated with steel plate in the housing and in the base areas, the base areas being drainboards, tanks and grills covering the tanks.
In thirty years of observations I have found that even stainless steel deteriorates, shortening the life of the washer unit. Although deterioration occurs around such openings as access doors and sumps, examinations over this period revealed that the highest rate of degradation occurs in the housing above the base. Quite surprisingly, it was found that the worst deterioration occurred in the rinse stages. Even more unexpectedly it was realized that the areas subject to extreme corrosion were those in which a high interchange of air and water vapor occurred, apparently leading to greater oxidation. At any rate the mixture of residual chemicals, moisture and air appears to accelerate the corrosion of the housing. Our study also revealed that attrition diminished from the top down, being less pronounced toward the lower portions of the housing, and nominal in the drainboard and tank areas which are subjected to liquid flow.
Various modifications to multistage washers have been suggested over the years to overcome housing corrosion, but they have not performed without limitations. Use of plastic walls has been unsuccessfully attempted due to the fact that high temperatures are used in some stages and that plastic expands four times as much as steel. Accordingly suggested remedies have been along other lines, such as construction of stainless steel, and housing coatings of various types.
The corroded housing could be replaced with stainless steel. However, given the size of these multistage washers, which are as usually as large as a railroad boxcar, this would be tantamount to a prohibitively expensive unit replacement. Resinous interior housing coating materials such as epoxies, polyesters, PVC linings and the like also have their drawbacks. Besides the added expense their use leads to future problems. Lining disintegration and loss of adhesion are common under conditions of use. When the coatings do break down, resulting contamination of the washer creates more severe problems than no coating protection at all.
Since operating conditions do lead to a high incidence of housing corrosion, it has long been my desire to find a commercially acceptable solution to that corrosion problem which will extend the life of multistage washers. As indicated, although coating of the housing with a resin is possible, such a solution leads to future problems. Plastic walls have been tried, but they too were discarded as unsuccessful because of expansion difficulties. Hence, industrial washers of the type discussed remain subject to improvement. This invention provides a life-extending solution to the problem, leading to the provision of industrial washers at no added cost.